BACKGROUND AND PURPOSE: ASCOD phenotyping (A, atherosclerosis; S, small vessel disease; C, cardiac pathology; O, other causes; and D, dissection) assigns a degree of likelihood to every potential cause (1 for potentially causal, 2 for causality is uncertain, 3 for unlikely causal but disease is present, 0 for absence of disease, and 9 for insufficient workup to rule out the disease) commonly encountered in ischemic stroke. We used ASCOD to investigate the overlap of underlying vascular diseases and their prognostic implication. METHODS: A single rater applied ASCOD in 405 patients enrolled in the Asymptomatic Myocardial Ischemia in Stroke and Atherosclerotic Disease study. RESULTS: A was present in 90% of patients (A1=43% and A2=15%), C in 52% (C1=23% and C2=14%), and S in 66% (S1=11% and S2=2%). On the basis of grades 1 and 2, 25% of patients had multiple underlying diseases, and 80% when all 3 grades were considered. The main overlap was found between A and C; among C1 patients, A was present in 92% of cases (A1=28%, A2=20%, and A3=44%). Conversely, among A1 patients, C was present in 47% of cases (C1=15%, C2=15%, and C3=17%). Grades for C were associated with gradual increase in the 3-year risk of vascular events, whereas risks were similar across A grades, meaning that the mere presence of atherosclerotic disease qualifies for high risk, regardless the degree of likelihood for A. CONCLUSIONS: ASCOD phenotyping shows that the large overlap among the 3 main diseases, and the high prevalence of any form of atherosclerotic disease, reinforces the need to systematically control atherosclerotic risk factors in all ischemic strokes.